/*
 * Copyright (c) 1999-2003, Carnegie Mellon University. All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 
 * 3. Products derived from the software may not be called "iVProg",
 *    nor may "iVProg" appear in their name, without prior written
 *    permission of Carnegie Mellon University.
 * 
 * 4. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes software developed by Carnegie Mellon University"
 */

package edu.cmu.cs.stage3.alice.core;

public abstract class Expression extends Element {

 public abstract Object getValue();
 public abstract Class getValueClass();
 private java.util.Vector m_expressionListeners = new java.util.Vector();
 private edu.cmu.cs.stage3.alice.core.event.ExpressionListener[] m_expressionListenerArray = null;

 public void addExpressionListener (edu.cmu.cs.stage3.alice.core.event.ExpressionListener expressionListener) {
  m_expressionListeners.addElement( expressionListener );
  m_expressionListenerArray = null;
  }

 public void removeExpressionListener (edu.cmu.cs.stage3.alice.core.event.ExpressionListener expressionListener) {
  m_expressionListeners.removeElement( expressionListener );
  m_expressionListenerArray = null;
  }

 public edu.cmu.cs.stage3.alice.core.event.ExpressionListener[] getExpressionListeners () {
  if (m_expressionListenerArray==null) {
   m_expressionListenerArray = new edu.cmu.cs.stage3.alice.core.event.ExpressionListener[m_expressionListeners.size()];
   m_expressionListeners.copyInto( m_expressionListenerArray );
   }
  return m_expressionListenerArray;
  }

 protected void onExpressionChange () {
  edu.cmu.cs.stage3.alice.core.event.ExpressionEvent expressionEvent = new edu.cmu.cs.stage3.alice.core.event.ExpressionEvent( this );
  java.util.Enumeration enu = m_expressionListeners.elements();
  while ( enu.hasMoreElements()) {
   edu.cmu.cs.stage3.alice.core.event.ExpressionListener expressionListener = (edu.cmu.cs.stage3.alice.core.event.ExpressionListener)enu.nextElement();
   expressionListener.expressionChanged( expressionEvent );
   }
  }

 }
